The organ itself is strong, has not shown signs of rejection, and has even grown 11 centimeters since it had been transplanted, according to the researchers.

Ciaran was born with a rare condition known as Long Segment Tracheal Stenosis, marked by a small windpipe that does not grow and can restrict breathing. He underwent the stem cell transplant in March 2010 after a standard trachea transplant did not work.

Researchers at the Great Ormond Street Hospital for Children, the Karolinska Institute in Stockholm and the University College London, stripped cells from a donor trachea and then used Ciaran's own bone marrow stem cells to rebuild the airways in the body. They also infused growth proteins to generate the tissue lining.

Using a patient's own stem cells not only could help to rebuild the fragile tissue, but also potentially could bypass the risk of having the organ rejected. A trachea is considered a difficult tissue to grow and transplant since it has a limited blood supply, according to Dr. Bill Putnam, professor and chair of the department of thoracic surgery at Vanderbilt University Medical Center, who was not involved in the research.

"I don't think there's anything standard about a tracheal transplant," said Putnam. "The fact that this single patient has survived for two years is worthy of notice."

Once the trachea was transplanted, the researchers continued to infuse growth proteins into the organ to continue stem cell generation. This technique allowed for researchers to transplant the organ faster instead of having to wait for the organ to grow outside of the body.

"Because the protocol used in this study was devised in an emergency, we applied empirically a new combination of technologies on the basis of previous clinical successes in non-airway settings," the researchers wrote, citing bioengineering techniques previously used to regenerate bone, nerves, and skin.

"We need more research on stem cells grown deliberately inside the body, rather than grown first in a laboratory over a long time," said Dr Martin Birchall, professor of Laryngology at the University College London, and co-author of the paper. "This research should help to convert one-off successes such as this into more widely available clinical treatments for thousands of children with severe tracheal problems worldwide."

Dr. Paolo Macchiarini, director of the Advanced Center for Translational Regenerative Medicine at the Karolinska Institute in Stockholm -- who was the head surgeon in this case -- and his team have been performing the transplants since 2008, when they transplanted a trachea using adult stem cells on a woman in Barcelona who suffered from tuberculosis.

In January 2012, the first U.S. patient underwent a stem cell trachea transplant.

While the procedure seems to have worked in a few patients, many experts said the method is still in the earliest stages of development.
"You never know what to do or how to interpret a success when it's one success," said Dr. Larry Goldstein, director of the stem cell program at University of California San Diego. "The question you grapple with is whether this treatment is going to be good with a larger number of people with this disease."

According to Putnam, should the treatment work for a wider group, the challenge may be in delivering such a specialized processed to a large number of people.
"There's a lot of infrastructure that has to be established to grow these cells and maintain the tracheal scaffolds," said Putnam. "You can't get these off the shelves; they have to be individually constructed which takes time and effort."